(1) Field of the Invention
The invention relates to a process for recovering thermoplastic polymers, and particularly linear polyester polymers from polyester fibers or other linear polymeric products in the form of collections of polyester fibers, yarns, or fabrics, including dyed polyester fibers, and preferably starting with waste polyester fabrics, for use in production of new undyed thermoplastic polyester products. More specifically, the invention relates to a process for recovering polyester polymer by means of stripping the dye from dyed polyester fibers with a solvent; subsequently dissolving the polyester fibers in a solvent; thereafter recovering the polymer without precipitation thereof by evaporation of the solvent from the molten polymer.
(2) Prior Art
The consumption of thermoplastic polymers is greater than ten billion pounds per year. Some, such as polyethylene, polypropylene, polyvinylchloride, polystyrene, polyamides and polyester, surpass the billion pounds per year rate. The use of many of these relatively expensive thermoplastic polymers in synthetic fibers has also increased tremendously. It has been estimated that the world's consumption of synthetic fibers will reach some 12 million metric tons (26 billion pounds) by the year 1980, of which 4.6 million metric tons would constitute polyester fibers, 4.1 million metric tons would be polyamide fibers and 2.3 million metric tons will be polyacrylic fibers (Chemical and Engineering News, Feb. 2, 1970, p. 22).
Concomitantly the world is facing a shortage of raw materials for thermoplastic polymers, and sophisticated and efficient methods of recycling are needed.
Various methods have been described in the prior art for the recovery of thermoplastic polymer, including polyester polymers, from scrap polymer. Waste fibers, films, yarns and fabrics have also been garnetted and reprocessed for various uses including the manufacture of yarn and fabrics. Other methods of recovery include the dissolution of the polymer in various solvents; thereafter precipitating and recoverying the polymer. The objects of such processes were to avoid polymer degradation and/or to separate from the usable polymer the degraded polymer and/or monomers as impurities. These processes were slow and expensive, suitable only for laboratory usage. Moreover, they neither addressed themselves to nor did they solve dye removal problems.
Neither the prior art fabric recovery processes nor the polymer recovery processes have provided for efficient dye stripping in conjunction with polymer recovery, and most have not addressed the problem.
It will thus be recognized that a satisfactory and efficient process for recovery of polyester polymer from polyester polymer, fibers or fabric, would be a meritorious advance in the art. It would substantially reduce the raw material requirement for the world's largest fiber market.